because they don't know how to demand taxes from this, and still fear for the economy of the country
They also fear that people would really put all their money to bitcoin not on the bank. As they cannot touch bitcoin they would probably banned this. Since it is a decentralized organization and government can't really touch them all they have to do is banned them. I'm afraid when it comes to our country as well.
In case of paper money there are different types of tax which are implemented on money of the people like withholding tax, sale tax or other taxes but in case of bit coin it was a fear that the people will keep all their money in the shape of bit coin so their banks will stop working.